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THYROID AND OTHER ENDOCRINE EMERGENCIES

This chapter addresses several common endocrine emergencies that may be seen in pregnant women. While most endocrine conditions can become emergencies if ignored or untreated, the intention of this chapter is not to exhaustively review endocrine complications in pregnancy; rather, the conditions that might realistically be faced in an ICU situation have been highlighted. These include thyrotoxicosis and thyroid storm, hypothyroidism and myxedema coma, addisonian crisis, pheochromocytoma, primary hyperalderonism, and diabetes insipidus. Diabetes mellitus and ketoacidosis have been dealt with elsewhere.

Thyroid Disease

Thyroid disease is the second most common endocrine condition affecting women of reproductive age. It is now common for obstetricians to care for women who enter pregnancy with an established thyroid deficiency or overactivity state. Because pregnancy in and of itself affects thyroid function, even women who are well-controlled prepregnancy may become uncontrolled requiring continued monitoring and adjustment. In addition, it is important to remember that the developing fetus may be at significant risk from circulating maternal antibodies that are no longer an issue for the mother. Despite the fact that hyperthyroidism is uncommon during pregnancy (0.2% of pregnancies) and thyroid storm is considered rare, vigilance is important because of the potential for significant morbidity and mortality in these conditions.

Definitions

Thyrotoxicosis is a generic term referring to a clinical and biochemical state resulting from overproduction of, and exposure to, thyroid hormone. The most common cause of thyrotoxicosis in pregnancy is Graves disease. This disorder is an autoimmune condition characterized by production of thyroid-stimulating immunoglobulin (TSI) and thyroid-stimulating hormone-binding inhibitory immunoglobulin (TBII) that act on the thyroid-stimulating hormone (TSH) receptor to mediate thyroid stimulation or inhibition, respectively.

Thyroiditis is caused by an autoimmune inflammation of the thyroid gland and may occur for the first-time postpartum. It is usually painless and may present as de novo hypothyroidism, transient thyrotoxicosis, or as initial hyperthyroidism followed by hypothyroidism within 1 year postpartum.

Physiology

Thyroxine (T4) is the major secretory product of the thyroid. The majority of circulating T4 is converted in the peripheral tissues to triiodothyronine (T3), the biologically active form of this hormone. T4 secretion is under the direct control of the pituitary TSH. The cell surface receptor for TSH is similar to the receptors for luteinizing hormone (LH) and human chorionic gonadotrophin (hCG). T4 and T3 are transported in the peripheral circulation bound to thyroxine-binding globulin (TBG), transthyretin (formerly called prealbumin), and albumin. Less than 0.05% of plasma T4 and less than 0.5% of plasma T3 are unbound and able to interact with target tissues. Routine T...